Conductive connection forming methods, oxidation reducing methods, and integrated circuits formed thereby

ABSTRACT

A conductive connection forming method includes forming a first layer comprising a first metal on a substrate and forming a second layer comprising a second metal different from the first metal on the first layer. At least a part of the first layer may be transformed to an alloy material comprising the first and second metals. A conductive connection may be formed to the alloy material. The alloy material may be less susceptible to formation of metal oxide compared to the first metal. By way of example, transforming the first layer may comprise annealing the first and second layer. An exemplary first metal comprises copper, and an exemplary second metal comprises aluminum, titanium, palladium, magnesium, or two or more such metals. The alloy material may be an intermetallic. A conductive connection may be formed to the alloy layer. An integrated circuit includes a semiconductive substrate, a layer comprising a first metal over the substrate, and a layer of alloy material within the first metal comprising layer. The alloy material layer may comprise the first metal and a second metal different from the first metal. The alloy material may be an intermetallic. A conductive connection may be formed on the alloy layer.

TECHNICAL FIELD

[0001] This invention relates to methods of forming conductiveconnections, methods of reducing oxidation, oxidation protectionmethods, methods of forming integrated circuit structures, such asconductive interconnects and wire bonds, and integrated circuits formedthereby.

BACKGROUND OF THE INVENTION

[0002] Several advantages exist for using copper metalization inintegrated circuits, such as semiconductor devices. However, coppermetalization may be more susceptible to oxidation under certain processconditions as compared to other metals, such as aluminum. Semiconductordevices often include at least two primary metal layers withinterconnections between such layers. The first metal layer can be aso-called “metal 1” layer and the second can be a so-called “metal 2”layer.

[0003] The first metal layer may be formed on a substrate and covered bya dielectric material, such as silicon dioxide. An opening for aninterconnect may then be formed through the dielectric material toexpose the first metal layer. The opening may be formed by patterning alayer of photoresist deposited over the dielectric and etching portionsof the dielectric material exposed through the photoresist. A commonprocess for removing photoresist comprises ashing. Such removal of aphotoresist exposes the first metal layer to the ashing conditions,potentially oxidizing the first metal layer. Copper is particularlysusceptible to oxidation at high temperature processing, such asprocessing at 200° C. or higher.

[0004] One method for reducing oxidation of the first metal layerincludes forming a layer of silicon nitride over the first metal layerprior to forming dielectric material over the, first metal layer. Thedielectric material is then processed as indicated above with formationof a photoresist, patterning of the photoresist, etching, andphotoresist removal by ashing. However, after etching an opening for aconductive interconnect, a separate etch of the silicon nitride may beused to expose the first metal layer preparatory to forming a conductiveinterconnect to such layer. A high level of selectivity may often beprovided for etching the silicon nitride compared to etching thedielectric material, such as silicon dioxide. The two-step etch processand highly selective etch of silicon nitride add a level of complexityto such processing that is undesirable.

[0005] Accordingly, new methods are desired for forming conductiveconnections between first and second metal layers in semiconductordevices that reduce oxidation of copper without introducing unduecomplexity to processing.

SUMMARY OF THE INVENTIONS

[0006] In one aspect of the invention, a conductive connection formingmethod includes forming a first layer comprising a first metal on asubstrate and transforming at least a part of the first layer to atransformed material comprising the first metal and a second substancedifferent from the first metal. A conductive connection may be formed tothe first layer by way of the transformed material. The method mayfurther include forming a second layer comprising a second metaldifferent from the first metal on the first layer. The transformedmaterial may be an alloy material comprising the first and secondmetals. The alloy material may be less susceptible to formation of metaloxide compared to the first metal. By way of example, transforming thefirst layer may comprise annealing the first and second layer. Anexemplary alloy includes an intermetallic. An exemplary first metalcomprises copper, and an exemplary second metal comprises aluminum,titanium, palladium, magnesium, or two or more such metals.

[0007] Further, another aspect of the invention includes a conductiveconnection forming method wherein a first layer comprising copper isformed over a substrate. A second layer of a second metal different fromthe copper may be formed over the first layer. At least some of thesecond metal may be incorporated into an intermetal layer comprising thesecond metal and copper. The method further includes removing at least aportion of any second metal not incorporated into the intermetal layerand exposing the intermetal layer. A conductive connection may be formedto the intermetal layer.

[0008] Such methods may be used as oxidation reducing methods or methodsfor protecting metal containing material from oxidation duringsemiconductor processing. Such methods are also conducive to use inmethods of forming integrated circuit interconnects or integratedcircuit wire bonds.

[0009] In another aspect of the invention, an integrated circuitincludes a semiconductive substrate, a layer, comprising a first metalover the substrate, and a layer of alloy material within the first metalcomprising layer. The alloy material layer may comprise the first metaland a second metal different from the first metal. A conductiveconnection may be formed on the alloy layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0011]FIG. 1 shows a fragmentary sectional view of a semiconductivewafer at one step of a method according to one aspect of the invention.

[0012]FIG. 2 shows the semiconductive wafer fragment of FIG. 1 at a stepsubsequent to that shown in FIG. 1.

[0013]FIG. 3 shows the semiconductive wafer fragment of FIG. 1 at a stepsubsequent to that shown in FIG. 2.

[0014]FIG. 4 shows the semiconductive wafer fragment of FIG. 1 at a stepsubsequent to that shown in FIG. 3.

[0015]FIG. 5 shows the semiconductive wafer fragment of FIG. 1 at analternative step subsequent to that shown in FIG. 3.

[0016]FIG. 6 shows the semiconductive wafer fragment of FIG. 1 at a stepsubsequent to that shown in FIG. 4.

[0017]FIG. 7 shows a fragmentary sectional view of a semiconductivewafer at one step of a method according to another aspect of theinvention.

[0018]FIGS. 8-12 each show the semiconductive wafer fragment of FIG. 7at successive steps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0020] In one aspect of the present invention, a conductive connectionforming method includes forming a first layer comprising a first metalon a substrate. In the context of this document, layers or materials“comprising metal” or “metal-comprising” layers or materials are definedto mean any layer or material containing at least one metallic element,regardless of whether the layer or material exhibits metallicproperties. For example, a metal-comprising layer or material may be ametal oxide, nitride, sulfide, or other substance even though suchsubstance might not exhibit metallic properties.

[0021] Turning to FIG. 1, a wafer portion 10 is shown having aninsulation layer 12 and a metal-comprising layer 14 formed on insulationlayer 12. Wafer portion 10 of FIG. 1 is one example of a first layercomprising a first metal formed on a substrate. Metal-comprising layer14 may be a variety of structures and compositions having a variety offunctions. Metal-comprising layer 14 can comprise copper, aluminum,another metal, or two or more such metals. Further, layer 14 may consistessentially of one or more metallic elements, such as the metals andmetal combinations listed above. In alternative to FIG. 1, insulationlayer 12 may comprise other materials, such as semiconductive orconductive materials. Further, even though FIG. 1 shows metal-comprisinglayer 14 and insulation layer 12 as part of wafer portion 10, theinvention is applicable to a variety of substrates and technology areas.Wafer portion 10 may comprise part of a semiconductor device, anintegrated circuit device, or other devices and apparatuses.

[0022] In the context of this document; the term “semiconductorsubstrate” or “semiconductive substrate” is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above.

[0023] Accordingly, metal-comprising layer 14 may be formed over asemiconductive substrate. After formation of metal-comprising layer 14,a second layer comprising a second metal different from the first metalin metal-comprising layer 14 may be formed on metal-comprising layer 14.FIG. 2 shows a metal-comprising layer 16, comprising a second metal,formed on metal-comprising layer 14. Metal-comprising layer 16 mayinclude, for example, aluminum, titanium, palladium, magnesium, anothermetal, or two or more such metals. Further, layer 16 may consistessentially of one or more metallic elements, such as the metals andmetal combinations listed above. Layers 14 and 16 may comprise, inaddition to metallic elements, non-metallic elements, depending on theparticular application of the present invention and processingconditions. Metal-comprising layer 16 may have a thickness of about 150to about 800 Angstroms. Preferably, metal-comprising layer 16 may have athickness of about 400 to about 500 Angstroms.

[0024] The present aspect of the invention further includes transformingat least a part of the first layer to an alloy material comprising thefirst and second metals. Alternatively, the present aspect of theinvention may include incorporating at least some of the second metalinto an alloy layer comprising the second metal and the first metal. Theindicated transforming may comprise annealing the first and secondlayer. Similarly, the indicated incorporating may also compriseannealing the first and second layer. Annealing may occur at atemperature of about 400° C. to about 500° C. The alloy material mayconsist essentially of the first and second metals. Also, the alloymaterial may comprise an intermetallic material. In the context of thisdocument, an “intermetallic” material is a type of metal alloy whereinthe constituents are held together by metallic bonding. Alloys alsoinclude other materials that are not held together by metallic bonding.An intermetallic material may exhibit properties as described below thatare advantageous in the present invention. However, it is alsoconceivable that alloys may exist that exhibit similar properties, butare not intermetals. Although the aspects of the invention are discussedherein primarily with reference to intermetals, one of ordinary skillwill appreciate that alloys that are not intermetals may also besuitable.

[0025] Turning to FIG. 3, an intermetallic material 18 is shown as aresult of transforming part of metal-comprising layer 16 to anintermetallic material comprising the first and second metals of layers14 and 16, respectively. In the present aspect of the invention, about50 to about 300 Angstroms of metal-comprising layer 14 may betransformed to the intermetallic material or, preferably, about 150Angstroms. A variety of thicknesses for intermetallic material 18 areconceivable and may be desired, depending on the application of theinvention as described herein or otherwise. FIG. 3 shows thatintermetallic material 18 exists beyond the original thickness of firstmetal layer 14. It is also conceivable that forming intermetallicmaterial 18 will not add substantially to the original thickness offirst metal layer 14.

[0026] It is preferred that intermetallic material 18 consistessentially of the first metal of layer 14 and the second metal of layer16. It is also preferred that intermetallic material 18, or anotheralloy material, exhibit the property of being less susceptible to theformation of metal oxide in comparison to the first metal of layer 14.Such a property, as well as other properties, may allow intermetallicmaterial 18 to reduce oxidation of metal-comprising layer 14 duringsubsequent processing. Oxidation of metal-comprising layer 14 canpotentially reduce the conductivity of conductive connections formed tometal-comprising layer 14. Accordingly, the present aspect of theinvention further includes forming a conductive connection to theintermetallic material, or another alloy material. Examples of aconductive connection include an integrated circuit interconnect, anintegrated circuit wire bond, and other structures.

[0027] Intermetallic material 18, or another alloy material, may alsoadvantageously exhibit the property of having approximately the sameresistivity as metal-comprising layer 14. Examples of particularlyadvantageous intermetallic materials include intermetals of titanium oraluminum with copper, specifically, TiCu₃. Such intermetals exhibitapproximately the same resistivity as copper. Such intermetals are alsomuch less susceptible to formation of metal oxide compared to copper.Accordingly, providing such intermetals as intermetallic material 18 mayreduce the oxidation of copper in processing subsequent to formation ofsuch intermetal.

[0028] Depending on the particular application of the invention, it maybe desirable to remove some portion of metal-comprising layer 16,intermetallic material 18, and/or metal-comprising layer 14. A varietyof processing scenarios are conceivable, For example, substantially allof metal-comprising layer 16 not comprised by intermetallic material 18may be removed. FIGS. 4 and 5 both present examples of such removal. InFIG. 4, the portion of intermetallic material 18 beyond the originalthickness of metal-comprising layer 14 is shown removed along withsubstantially all of metal-comprising layer 16. Such a removal leavesbehind only the portion of intermetallic material 18 formed withinmetal-comprising layer 14. Such removal may be accomplished by a varietyof processes.

[0029] A non-selective etch or chemical mechanical polishing are twoexamples of potential processes. As shown in FIG. 4, such processes, aswell as other processes, may be used to also remove any portion ofmetal-comprising layer 16 not comprised by the intermetallic material.Removing “substantially” all of a material may allow insignificantportions of such material to remain provided that the central objectiveof the removal is accomplished. One possible objective for removingmetal-comprising layer 16 is to prevent electrical shorts between otherconductive structures, such as the two portions of metal-comprisinglayer 14 shown in FIGS. 1-6.

[0030] In alternative to the above-described methods, the objective ofavoiding electrical shorts, as well as other objectives, may be met byinstead removing at least some of metal-comprising layer 16 notcomprised by intermetallic material 18. A sufficient thickness ofintermetallic material 18 may be left behind to reduce oxidation ofmetal-comprising layer 14. The potential additional objective ofexposing intermetallic material 18 may be met by such an alternativeprocess as well as by the other previously mentioned processes forremoving metal-comprising layer 16.

[0031] Turning to FIG. 5, an alternative structure is shown that mayresult from the latter-mentioned processes for removing metal-comprisinglayer 16. In FIG. 5, substantially all of metal-comprising layer 16 isremoved without removing a substantial portion of intermetallic material18. Not removing a “substantial” portion at a material means that if anyremoval occurs, such removal is not sufficient to prevent the centralobjective of providing such material. Such a removal process may beaccomplished by a selective etch of metal-comprising layer 16 inpreference to intermetallic material 18. The selectivity ratio of layer16 removal to material 18 removal may greater than 5 to 1, for example,approximately 10 or more to 1. One potential selective etch includesexposure of metal-comprising layer 16 to a halogenated acid, such as HFor HCl, or other acids, such as H₂SO₄ and HNO₃, or combinations thereof.Such exposure may be effective to remove either titanium or aluminummetal substantially selectively to copper intermetals with titanium oraluminum. A conductive connection may then be formed to the exposedintermetal material 18 as described above. It is also conceivable withinthe present aspect of the invention that some portion ofmetal-comprising layer 16 will remain, rather than removingsubstantially all of such material. For example, only a portion ofmetal-comprising layer 16 sufficient to expose intermetallic material 18may be removed, still allowing formation of a conductive connection.

[0032] Another aspect of the invention includes an oxidation reducingmethod wherein a layer comprising a first metal may be contacted with asecond metal different from the first metal while treating the layer incontact with the second metal. The method includes forming anintermetallic material at least partially within the layer, theintermetallic material comprising the first and second metals. Further,substantially all of any residual second metal not comprised by theintermetallic material may be removed from over the intermetallicmaterial. A conductive connection to the intermetallic material may beformed without forming a substantial amount of metal oxide on the firstmetal. Treating the layer in contact with the second metal may compriseannealing the layer. From the text associated with FIGS. 1-5 above, itcan be seen that such figures provide one example of an oxidationreducing method.

[0033] In an oxidation protection method, also exemplified by FIGS. 1-5,metal-containing material may be protected during semiconductorprocessing. A first metal-containing material may be formed over asubstrate followed by a second metal-containing material over the firstmetal-containing material. Annealing the first and secondmetal-containing materials may form an intermetal material from some ofthe first material and some of the second material. After annealing, theintermetal material may be exposed to conditions effective to oxidizethe first metal-containing material, but the intermetal material mayprotect at least some of the first metal-containing material fromoxidation during the exposing.

[0034] Turning to FIG. 6, a structure 60 formed by an integrated circuitinterconnect forming method is exemplified, illustrating yet anotheraspect of the invention. In FIG. 6, metal-comprising layer 64 comprisesa first level of integrated circuit wiring formed over an insulationlayer 62 over a semiconductive substrate (not shown). Intermetallicmaterial 68, or another alloy material, is formed at least partiallywithin such first wiring level and intermetallic material 68 comprises afirst metal from metal-comprising layer 64 and a second metal differentfrom the first metal. A conductive interconnect 65 is shown formedthrough an insulation layer 63 in electrical contact with intermetallicmaterial 68. Conductive interconnect 65 may be formed on intermetallicmaterial 68.

[0035] In the present aspect of the invention, forming intermetallicmaterial 68 may comprise forming a layer comprising the second metal onthe first wiring level. One example is shown in FIG. 2 whereinmetal-comprising layer 16 is formed on metal-comprising layer 14.Forming the intermetallic material may further include annealing thelayer and first wiring level and removing at least some of any secondmetal not comprised by the intermetallic material. A sufficientthickness of intermetallic material may be left behind to reduceoxidation of the first wiring level where conductive interconnect 65connects to the first wiring level.

[0036]FIG. 6 shows conductive interconnect 65 formed from the samematerial as a second level 66 of integrated circuit wiring. Such astructure may be produced by forming second wiring level 66 over firstwiring level 64 during formation of conductive interconnect 65. A dualdamascene process or similar process known to those skilled in the artmay accomplish formation of such a structure.

[0037] Another aspect of the present invention includes an integratedcircuit wire bond forming method. Such method involves formingintegrated circuit wiring and defining a bond pad in the wiringcomprising a first metal. An intermetallic material may be formed atleast partially within the bond pad, the intermetallic materialcomprising the first metal and a second metal different from the firstmetal. A wire bond may be formed in electrical contact with theintermetallic material.

[0038] Turning to FIGS. 7-12, one example of the integrated circuit wirebond forming method is illustrated. FIG. 7 shows a wafer portion 70including an insulation layer 72 and integrated circuit wiring 78 formedin insulation layer 72. Opening 74 formed in insulation layer 72 exposesa portion of integrated circuit wiring to allow formation of additionalwiring within opening 74. Opening 76 is formed in insulation layer 72,exposing integrated circuit wiring 78 to allow formation of a bond pad.In FIG. 8, bond pad opening 76 is extended further into insulation layer72 forming extended bond pad opening 80. In FIG. 9, a layer ofconductive material 82 comprising a first metal is formed over waferportion 70 to provide conductive material for additional wiring inwiring opening 74 and a bond pad in extended bond pad opening 80.

[0039] As shown in FIG. 10, a layer 84 comprising a second metal may beformed over conductive layer 82. Formation of second-metal-comprisinglayer 84 allows formation of an intermetallic material at leastpartially within the portion of conductive layer 82 within extended bondpad opening 80. Formation of an intermetallic material may beaccomplished within extended bond pad opening 80 using processes asdescribed herein. In one such process, layer 84 and conductive layer 82within bond pad opening 80 are annealed. Such annealing produces waferportion 70 shown in FIG. 11 having intermetallic material 86, or anotheralloy material, at least partially within conductive layer 82 withinbond pad opening 80. At least some of any second metal not comprised bythe intermetallic material may be removed, leaving a sufficientthickness of intermetallic material to reduce oxidation of a bond padwhere a wire bond contacts such bond pad.

[0040] In FIG. 11, substantially all of second-metal-comprising layer 84is comprised by intermetallic material 86. Such a feature may bepracticed with any of the aspects of the invention disclosed herein.That is, substantially all of a thickness of a layer comprising a secondmetal that exists over a layer comprising a first metal may betransformed to an intermetallic material. In this manner, onlyintermetallic material, rather than excess second metal from thesecond-metal-comprising layer will exist over a first-metal-comprisinglayer.

[0041] Turning to FIG. 12, excess portions of intermetallic material 86and conductive layer 82 are shown removed from wafer portion 70. Suchremoval forms additional integrated circuit wiring 88 from conductivelayer 82 within wiring opening 74. Such removal also forms bond pad 90from intermetallic material 86 and conductive layer 82 within bond padopening 80. At least one of the effects of extending bond pad opening 76into insulation layer 72 is formation of bond pad 90 having an outersurface that is topographically below immediately surroundingstructures. By extending bond pad opening 76 less deep into insulationlayer 72, the outer surface of bond pad 90 may be made level withimmediately surrounding structures but still comprise intermetallicmaterial 86. Defining a bond pad as described may provide easy removalof intermetallic material 86 by planarization methods, for examplechemical mechanical polishing, from all areas except over conductivelayer 82 within bond pad opening 80.

[0042] As also seen in FIGS. 9-12, such processing also providesintermetallic material 86 at least partially within bond pad 90. Asdiscussed above regarding other aspects of the invention, intermetallicmaterial may exhibit a property of resistance to oxidation duringsemiconductor processing. Accordingly, formation of conductivitylimiting metal oxide may be reduced when forming a wire bond 92 to bondpad 90. Such is even true when bond pad 90 and wire bond 92 comprisecopper.

[0043] In the aspects of the invention described above, a transformedmaterial, such as an alloy material or another material, may be formedby still other methods. A conductive connection forming method caninclude transforming at least a part of metal-comprising layer 14 to atransformed material by ion implanting. Implanting a second substancedifferent from the metal in metal-comprising layer 14 may impart adecreased susceptibility in the transformed material to oxidationcompared to the metal. For example, nitrogen or another substance may beimplanted into metal-comprising layer 14 to an extent sufficient todecrease oxidation. The nitrogen implant may be sufficiently limited inamount and depth such that a conductive connection may still be formedto the metal-comprising layer 14 by way of the transformed material.Limiting the implant energy may produce a shallow implant ofmetal-comprising layer 14, thus also limiting any impact on conductivityof metal-comprising layer 14.

[0044] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-54. (canceled).
 55. An integrated circuit comprising: a semiconductivesubstrate; a layer comprising Cu over the substrate; a layer of alloymaterial within the layer comprising Cu the alloy material layercomprising intermetallic Cu₃Ti; and a conductive connection on the alloylayer.
 56. The integrated circuit of claim 55 wherein the alloy materialconsists essentially of Cu₃Ti.
 57. The integrated circuit of claim 55wherein about 50 to about 300 Angstroms of the first metal layer isalloy material.
 58. The integrated circuit of claim 55 wherein theconductive connection comprises an integrated circuit via or anintegrated circuit wire bond.
 59. The integrated circuit of claim 55wherein a thickness of the alloy material layer is sufficient to reduceoxidation of the layer comprising Al.